Method of manufacturing a laminated structure

ABSTRACT

The invention relates to a method of manufacturing a laminated structure. The method comprises the steps of: providing at least a first and a second flexible structure; applying a coating on at least a part of said first and said second flexible structure to obtain a first coated flexible structure and a second coated flexible structure; bringing the coated surface of said first coated flexible structure and the coated surface of said second coated flexible structure together and pressing said first coated flexible structure and said second coated flexible structure together to create a cold welding between said first coated flexible structure and said second coated flexible structure. The invention further relates to a laminated structure comprising a first flexible structure and a second flexible structure being bonded by means of a cold welding.

FIELD OF THE INVENTION

The invention relates to a method of manufacturing a laminatedstructure.

The invention further relates to a laminated structure obtained by thismethod and to the use of such a laminated structure as capacitor orsuperconductor.

BACKGROUND OF THE INVENTION

In order to obtain a laminated structure of two coated flexiblesubstrates, one often uses an adhesive such as a glue or an organicresin.

However, this method has the drawback that the coating can be damaged bythe adhesive.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method ofmanufacturing a laminated structure thereby avoiding the problems of theprior art.

It is a further object to provide a laminated structure and the use ofsuch a laminated structure as capacitor or superconductor.

According to a first aspect of the present invention, a method ofmanufacturing a laminated structure is provided. The method comprisesthe steps of

-   -   providing at least a first and a second flexible structure;    -   applying a coating on at least a part of the first and the        second flexible structure to obtain a first coated flexible        structure and a second coated flexible structure;    -   bringing the coated surface of the first coated flexible        structure and the coated surface of the second coated flexible        structure together and pressing the first coated flexible        structure and the second coated flexible structure together to        create a cold welding between the first coated flexible        structure and the second coated flexible structure.

The coating on the first and the second flexible structure can beapplied by any technique known in the art as for example wet chemicaldeposition techniques or vacuum deposition techniques.

Preferably, the coating on the first and the second flexible structureis applied by means of vacuum deposition techniques such as sputtering,for example magnetron sputtering, ion beam sputtering and ion assistedsputtering, evaporation, laser ablation or chemical vapor depositionsuch as plasma enhanced chemical vapor deposition.

The metal coating may comprise any metal or metal alloy. Preferred metallayers comprise for example Al, Ti, V, Cr, Co, Ni, Cu, Zn, Rh, Pd, Ag,In, Sn, Ir, Pt, Au, Pb or alloys thereof.

Preferably, the coating applied on the first flexible structure isIdentical to the coating applied on the second flexible structure.

The coating on the first flexible structure and the coating on thesecond flexible structure can be applied by one deposition source or bytwo different deposition sources. The application by one depositionsource is preferred.

A cold welding may occur when two dean metal surfaces are brought intointimate contact.

To obtain a cold welding, the metal surfaces have to be free ofcontamination, such as oxides, nitrides, absorbed gases or organiccontaminations. In addition, the metal surfaces have to be broughttogether under sufficient high mechanical force to bring the atoms atthe interface into intimate contact

The elimination of contamination can be obtained by cleaning the metalsurface.

In a preferred embodiment, the application of the coating and the coldwelding of the first and second coated flexible structure is performedin a vacuum without breaking the vacuum between the coating step and thecold welding step.

By maintaining the vacuum through the process steps, one prevents theformation of surface oxides and other contaminations.

Furthermore, by performing the different process steps in one processchamber, the need to relocate or otherwise move the flexible structuresbetween different process chambers is eliminated.

The first and the second flexible structure may comprise any flexiblesubstrate known In the art, as for example a flexible metal substrate ora flexible polymer substrate.

Preferred flexible metal substrates comprise for example metal tapes orfoils or metallized tapes or foils.

The metal comprises preferably steel, nickel or nickel alloys, ortitanium or titanium alloys.

The metal substrate preferably has a thickness between 1 and 100 μm, asfor example 10 μm.

Metallized tapes or foils comprise preferably a polymer tape or foilcoated on both sides with a metal layer.

Preferred flexible polymer substrates comprise for example polymer tapesor foils such as polyester (PET), polypropylene such as orientedpolypropylene (OPP) and bioriented polypropylene BOPP), polyetherimideor polyimide (for example known as Kapton® or Uppilex®) tapes or foils.

In a preferred embodiment, the first and/or the second flexiblestructure comprises a coated flexible substrate as for example a metaltape or foil or a metallized tape or foil coated with a ceramic layer ora polymer foil or tape coated with a metal layer.

The fist and the second flexible structure may comprise the samematerial or may comprise a different material.

The ceramic layer is preferably selected from the group consisting ofoxides, titanates, niobates, zirconates and high temperaturesuperconductors such as (Re)—Ba—Cu-oxides. (Re) may comprise one or morerare earth elements as for example Y or Nd.

Some common titanates used for capacitors comprise CaTiO₃, SrTiO₃,BaTiO₃ and PbTiO₃, (Ba,Sr)TiO₃, PbZr_((1-x))Ti_(x)O₃,Sr_((1-x))Bi_(x)TiO₃. Nb_(x)TiO₃, BiBi₂NbTiO₉, BaBi₄Ti₄O₁₅, Bi₄Ti₃O₁₂,SrBi₄Ti₄O₁₅, BaBi₄Ti₄O₁₅, PbBi₄Ti₄O₁₅ or PbBi₄Ti₄O₁₅.

Some niobates comprise CaBi₂Nb₂O₉, SrBi₂Nb₂O₉, BaBi₂Nb₂O₉, PbBi₂Nb₂O₉,(Pb,Sr)Bi₂Nb₂O₉, (Pb,Ba)Bi₂NbO₉, (Ba,Ca)Bi₂Nb₂O₉, (Ba,Sr)Bi₂Nb₂O₉,BaBi₂Nb₂O₉, PbBi₂Nb₂O₉, SrBi₂Nb₂O₉, Ba_(0.75)Bi_(2.25)Ti_(0.25)Nb_(1.75)O₉, Ba_(0.5)Bi_(2.5)Ti_(0.5)Nb_(1.5)O₉,Ba_(0.25)Bi_(2.75)Ti_(0.75)Nb_(1.25)O₉, Bi₃TiNbO₉,Sr_(0.8)B_(2.2)Ti_(0.2)Nb_(1.8)O₉, Sr_(0.6)Bi_(2.4)Ti_(0.4)Nb_(1.6)O₉.Bi₃TiNbO₉, Pb_(0.75), Bi_(2.25)Ti_(0.25)Nb_(1.75)O₉,Pb_(0.6)Bi_(2.5)Ti_(0.5)Nb_(1.5)O₉,Pb_(0.25)Bi_(2.75)Ti_(0.75)Nb_(1.25)O₉ or Bi₃TiNbO₉.

Common oxides comprise Ta₂O₅, SiO₂, Al₂O₃, TiO₂ and (Re)—Ba—Cu-oxides.

Also ceramic layers comprising lead zirconate titanate (PZT) and leadzirconate lanthanum modified titanate (PZLT) can be used.

The ceramic layer can be deposited by a number of different techniquessuch as sputtering for example magnetron sputtering, ion beam sputteringand ion assisted sputtering, evaporation, laser ablation, chemical vapordeposition or plasma enhanced chemical vapor deposition.

Possibly, the first and/or the second flexible structure comprise anintermediate layer layer between the flexible substrate and the ceramiclayer. This intermediate layer comprises for example a buffer layer. Thebuffer layer may comprise a metal layer such as a noble metal layer oran oxide layer such as yttrium stabilized zirconium layer, a CeO₂ layeror a Y₂O₅ layer.

The method as described above is in particular suitable to manufacturecapacitors or to manufacture superconductors.

A great advantage of the method according to the present invention isthat laminated structures can be manufactured without using organicadhesives such as glues.

It is known in the art that ceramic layers and more particularly ceramiclayers used for superconductors are brittle layers and may sufferseriously from cracking by bending the material.

The method according to the present invention allows to reduce thestress on the ceramic layer by putting the ceramic layer in a laminatedstructure. The ceramic layer can be brought close to the so-calledneutral axis by choosing the thickness of the different layers and/orthe Young's modulus of the different layer.

The neutral axis is defined as the axis of the layered structure whichunder bending undergoes neither compression nor elongation.

Furthermore, the method according to the present invention allows toobtain a good electrical and mechanical contact between the first andthe second flexible structure and the coating layer.

According to a second aspect of the present invention, a laminatedstructure is provided. The laminated structure comprises a firstflexible structure and a second flexible structure. The first flexiblestructure and the second flexible structure are bonded to each other bymeans of a metal layer. The metal layer is applied by applying a metalcoating on at least a part of the first flexible structure and byapplying a metal coating on at least a part of the second flexiblestructure, by bringing the coated surfaces of the first flexiblestructure and the second flexible structure together and by pressing thefirst flexible structure and the second flexible structure together tocreate a cold welding between the first flexible structure and thesecond flexible structure.

The metal coating forming the cold welding is free of contaminations.

The laminated structure according to the present invention does not makeuse of an organic adhesive such as a glue.

This is a great advantage as an organic adhesive may damage thesubstrate or the coating applied on the substrate.

According to a third aspect of the present Invention, the use of alaminated structure as capacitor Is provided.

A preferred capacitor is a wound capacitor comprising a laminatedstructure as described above.

Wound capacitors are known in the art. Generally, these capacitorscomprise a pair of metallized polymer films wound together into a roll.The metallized films are obtained by depositing a thin layer of aconductive material onto a polymer film.

However, this type of capacitors shows a number of drawbacks. Thepolymer films are characterized by a limited relative dielectricconstant ε_(r).

Also the thickness of the polymer film (dielectricum) can not be lowerthan a certain minimum value, generally 0.7 μm.

As the capacitance of a capacitor is determined as$c = {ɛ_{0}ɛ_{r}\frac{S}{d_{d}}}$with

-   S: the area of the capacitor;-   d_(d): the thickness of the dielectricum (the separation distance    between two metal layers);-   ε₀: the dielectric constant of vacuum;-   ε_(r): the relative dielectric constant of the dielectricum;    only moderate capaciance values can be reached.

Preferred wound capacitors according to the present invention comprise alaminated structure having a first and a second flexible substrate.

The first and the second flexible substrate comprise a metal substrateand a ceramic layer (dielectric layer). The ceramic layer is preferablydeposited by means of a vacuum deposition technique.

The first and the second flexible substrate are bonded to each other bymeans of a metal layer.

The metal layer is preferably applied by applying a metal coating on atleast a part of the first flexible structure and by applying a metalcoating on at least a part of the second flexible structure, by bringingthe coated surfaces of the first flexible structure and the secondflexible structure together and by pressing the first flexible structureand the second flexible structure together to create a cold weldingbetween the first flexible structure and the second flexible structure.

The coating on the first and the second flexible structure can beapplied by any technique known in the art as for example wet chemicaldeposition techniques or vacuum deposition techniques.

Preferably, the coating on the first and the second flexible structureis applied by means of vacuum deposition techniques such as sputtering,for example magnetron sputtering, ion beam sputtering and ion assistedsputtering, evaporation, laser ablation or chemical vapor depositionsuch as plasma enhanced chemical vapor deposition.

The metal coating may comprise any metal or metal alloy. Preferred metallayers comprise for example Al, Ti, V, Cr, Co, Ni, Cu, Zn, Rh, Pd, Ag,In, Sn, Ir, Pt, Au, Pb or alloys thereof.

Preferably, the coating applied on the first flexible structure isidentical to the coating applied on the second flexible structure.

The coating an the first flexible structure and the coating on thesecond flexible structure can be applied by one deposition source or bytwo different deposition sources. The application by one depositionsource is preferred.

A wound capacitor according to the present invention shows manyadvantages. Some of these advantages are related to the deposition ofthe ceramic layers.

First of all, dielectric material having a high relative dielectricconstant ε_(r) can be obtained by means of vacuum deposition. Asdescribed above the relative dielectric constant ε_(r) of the dielectricmaterial is preferably higher than 20.

However, dielectric materials with a relative dielectric constant ε_(r)that is much higher can be obtained.

Typical ranges of dielectric material are from 20 to 100, from 100 to1000, from 1000 to 10000, from 10000 to 20000 and even higher than20000.

A second advantage is that thin layers of dielectric layers can bedeposited.

The thickness of the dielectric material can be much lower than thethickness of the dielectric material (i.e. the thickness of polymerfilms) in the known metallized film capacitors.

The minimum thickness that can be reached in the known metallized filmcapacitors is generally accepted to be 0.7 μm.

By vacuum deposition layers of 0.001 μm can be deposited. Generally, thethickness of a vacuum deposited dielectric layer is between 0.001 and 10μm, as for example 1 μm, 0.1 μm or 0.01 μm.

Both the increase in the relative dielectric constant ε_(r) and thereduction of the thickness of the dielectric material have a positiveinfluence on the capacitance a capacitor.

A third advantage of a dielectric material deposited by a vacuumdeposition technique is the high quality of the dielectric material thatcan be obtained and that the ease to control the thickness of thedielectric material.

Furthermore by depositing a dielectric material on a metal substratehigher temperature can be reached compared with metallized polymerfilms.

In a wound capacitor according to the present invention, the first andthe second structure are bonded by means of a metal layer. This meansthat the use of organic adhesives such as a glue is avoided.

According to a fourth aspect of the present invention, the use of alaminated structure as superconductor is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described into more detail with reference tothe accompanying drawing wherein

FIG. 1 and FIG. 2 show schematic representations of the method accordingto the present invention to manufacture a lamiated structure;

FIG. 3 to 7 show different embodiments of capacitors;

FIG. 8 shows a laminated structure according to the present inventionused as high temperature superconductor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a schematic representation of the method according to thepresent invention. Two flexible structures 12 comprising a metal foilcoated with a ceramic layer are provided in a vacuum chamber. The twoflexible structures 12 are coated from a deposition source 16 with ametal coating layer 14. Subsequently, the two coated flexible structuresare united by pressing the laminated structure together between tworolls 18.

Between the two coated surface a cold welding is created.

The coating of the flexible structures 12 and the uniting of the twoflexible structures by means of the coating layer 14 is preferably donein the vacuum chamber without breaking the vaccum.

Possibly, the method may be followed by other processing steps such asheating, coating, slitting, another lamination process . . .

FIG. 2 shows a schematic representation of a method according to theinvention in which three flexible structures 22 are united by applying ametal coating 24 from deposition sources 26 between two consecutiveflexible structures 22 and by pressing the laminated structure togetherbetween two rolls 28.

For a person skilled In the art it is dear that the number of flexiblestructures of the laminated structure can be increased. Generally, thenumber of flexible structures of a laminated structure ranges between 2and 10.

FIGS. 3 to 7 show different embodiments of capacitors.

The flexible structures 31, 33 that are laminated are shown in FIGS. 3 ato 7 a.

FIGS. 3 b to 7 b show the laminated structure 35 comprising the flexiblestructures 31, 33 bonded to each other by means of metal coating layer36.

FIGS. 3 c to 7 c show a stack 37 of laminated structures 35 comprisingelectodes 39.

The flexible structures 31, 33 comprise a flexible substrate 40 and aceramic layer 42.

Possibly, one or both of the flexible structure 31 or 33 comprise abuffer layer 44 between the substrate 40 and the ceramic layer 42.

The buffer layer 44 comprises for example a metal layer such as a noblemetal layer for example Pd, Pt. Au or Ag.

An example of an embodiment comprising a buffer layer 44 In the firstand the second flexible structure is given in FIG. 5.

In the embodiments shown in FIG. 3 to 6, the flexible substratecomprises a metal tape or a metallized tape. In the embodiment shown InFIG. 7, the flexible substrate of the first flexible structure comprisesa polymer tape.

To show the attractiveness of a capacitor according to the presentinvention, the capacitance per volume of a capacitor according to thepresent invention is compared with the capacitance per volume of ametallized film capacitor known in the art.

The capacitance per volume is defined as:$\frac{C}{V} = \frac{ɛ_{0}ɛ_{r}}{d_{d}d_{cap}}$with

-   ε₀: the dielectric constant of vacuum;-   ε_(r) the relative dielectric constant ε_(r) constant of the    dielectric material;-   d_(d): the thickness of the dielectric material (the separation    distance between two metal layers);-   d_(cap): d_(d)+d_(e) (with d_(e) the thickness of the metal layer    (the electrode)).

A metallized film capacitor comprises a metallized polymer film woundinto a roll to form a capacitor. The metallized polymer film is formedby depositing a thin layer of a conductive material onto a polymer film.

The metallized film capacitor that is considered as an example comprisesa polymer film (dielectricum) having a relative dielectric constantε_(r1) of 3.

As thickness of the polymer mm d_(d1), the thinnest thickness known inthe art is considered: 0.7 μm.

In case the metal layer on the polymer film is deposited on the polymerfilm by means of sputtering, the thickness of a metal layer can beconsidered to be very low. Therefore, in the above calculation d isconsidered to be equal to d_(d1).

The capacitance per volume of the metalized film capacitor can becalculated as follows:$\frac{C_{1}}{V_{1}} = {\frac{ɛ_{0}ɛ_{r\quad 1}}{d_{d\quad 1}d_{d\quad 1}}.}$

As capacitor according to the present invention, a capacitor comprisinga first and a second structure each comprising a metal substrate and adielectric material deposited on this metal substrate is considered. Thedielectric material has a relative dielectric constant ε_(r 2) of 500, athickness of the dielectric material d_(d2) of 0.01 μm. The metalsubstrate (electrode) has a thickness of 10 μm.

The capacitance per volume is:$\frac{C_{2}}{V_{2}} = {\frac{ɛ_{0}ɛ_{2\quad r}}{d_{d\quad 2}d_{cap}}.}$

It can be concluded from the above mentioned examples that thecapacitance per volume of the second capacitor is about 800 times higherthan the capacitance per volume of the first capacitor.

It is dear that the above mentioned calculation may only be consideredas an example. As the relative dielectric constant ε_(r) of thedielectric material of a capacitor according to the present invnetioncan be much higher than the one taken in the example and as thethickness of the dielectric material can be lower than the thicknessconsidered in the example, capacitors with a much higher capacitance pervolume can be obtained according to the present invention.

FIG. 8 shows a laminated structure according to the present inventionused as high temperature superconductor.

High temperature superconductors (HTS) such as (Re)—Ba—Cu-oxides arebrittle ceramic materials. Cracking of the brittle superconductor layercan cause dramatic reduction of the current conduction capacity(critical current J_(c)). In order to avoid this reduction of J_(c), thebending radius of a non-laminated coated conductor has to be larger thana critical value that depends on the thickness of the HTS coating in alaminated structure, it should be possible to minimise the effect andthereby obtaining a conductor that can be bent to a smaller bendingradius. By putting the HTS coating in a laminated structure, it shouldbe possible to minimise the effect and thereby obtaining a conductorthat can be bent to a smaller bending radius.

FIG. 8 shows an example of a laminated structure 80 in which the bendingstress on the HTS Is minimal.

The laminated structure 80 comprises two flexible structures 81 and 82.Each flexible structure comprises a flexible substrate such as a metalfoil or a polymer foil 83, 84 and a HTS coating 85, 86. Between themetal foil 83, 84 and the HTS coating 85, 86 a buffer layer 87, 88 isdeposited. The two flexible structures 81 and 82 are united by means ofcoating layer 89.

By the presence of the flexible substrates 83, 84, the HTS coatings 85,86 are brought closer to the so-called neutral axis.

The neutral axis is determined by the thicknesses of the respectivelayers and by their Young's moduli ε.

1. A method of manufacturing a laminated structure, said methodcomprising the steps of providing at least a first and a second flexiblestructure; applying a metal coating on at least a part of said first andsaid second flexible structure to obtain a first coated flexiblestructure and a second coated flexible structure; bringing the coatedsurface of said first coated flexible structure and the coated surfaceof said second coated flexible structure together and pressing saidfirst coated flexible structure and said second coated flexiblestructure together to create a cold welding between said first coatedflexible structure and said second coated flexible structure.
 2. Amethod according to claim 1, whereby said coating on said first and saidsecond flexible structure is applied by a vacuum deposition technique.3. A method according to claim 2, whereby the different process stepsare performed in vacuum without breaking said vacuum between the processsteps.
 4. A method according to claim 1, whereby said first and saidsecond flexible structure comprise a flexible metal substrate, aflexible polymer substrate or a flexible metallized polymer substrate.5. A method according to claim 1, whereby said first flexible structureand said second flexible structure comprise a coated flexible substrate.6. A method according to claim 5, whereby said coated flexible substratecomprises a metal foil or tape coated with a ceramic layer.
 7. A methodaccording to claim 6, whereby said ceramic layer is selected from thegroup consisting of oxides, titanates, niobates and zirconates.
 8. Amethod according to claim 6, whereby said ceramic layer comprises a hightemperature superconductor.
 9. A method according to claim 5, wherebysaid coated flexible substrate comprises a polymer foil or tape coatedwith a metal layer.
 10. A method according to claim 5, whereby saidfirst and/or said second flexible structure comprise an intermediatelayer between said flexible substrate and the coating applied on saidflexible substrate.
 11. A method according to claim 10, whereby saidintermediate layer comprises a buffer layer comprising a yttriumstabilized zirconium layer, a CeO₂ layer or a Y₂O₃ layer.
 12. Alaminated structure comprising a first flexible structure and a secondflexible structure, said first flexible structure and said secondflexible structure being bonded to each other by means of a metal layer,said metal layer being applied by applying a metal coating on at least apart of said first flexible structure and by applying a metal coating onat least a part of said second flexible structure, by bringing thecoated surfaces of said first flexible structure and said secondflexible structure together and by and by pressing said first flexiblestructure and said second flexible structure together to create a coldwelding between said first flexible structure and said second flexiblestructure.
 13. A laminated structure according to claim 12, whereby saidlaminated structure is glue free.
 14. A laminated structure according toclaim 12, whereby said flexible substrate comprises a flexible metalsubstrate, a flexible polymer substrate or a flexible metallized polymersubstrate.
 15. A laminated structure according claim 12, whereby saidfirst flexible structure and said second flexible structure comprise acoated flexible substrate.
 16. A laminated structure according to claim15, whereby said coated flexible substrate comprises a metal foil ortape coated with a ceramic layer.
 17. A laminated structure according toclaim 16, whereby said ceramic layer is selected from the groupconsisting of oxides, titanates, niobates and zirconates.
 18. Alaminated structure according to claim 16, whereby said ceramic layercomprises a high temperature superconductor.
 19. A laminated structureaccording to claim 15, whereby said coated flexible substrate comprisesa polymer foil or tape coated with a metal layer.
 20. A laminatedstructure according to claim 15, whereby said first and/or said secondflexible structure comprise an intermediate layer between said flexiblesubstrate and the coating applied on said flexible substrate.
 21. Alaminated structure according to claim 20, whereby said intermediatelayer comprises a buffer layer comprising a yttrium stabilized zirconiumlayer, a CeO₂ layer or a Y₂O₃ layer.
 22. A capacitor comprising alaminated structure as defined in claim
 12. 23. A capacitor according toclaim 22, whereby said capacitor is a wound capacitor comprising alaminated structure comprising a first flexible structure and a secondflexible structure, said first flexible structure and said secondflexible structure being bonded to each other by means of a metal layer,said metal layer being applied by applying a metal coating on at least apart of said first flexible structure and by applying a metal coating onat least a part of said second flexible structure, by bringing thecoated surfaces of said first flexible structure and said secondflexible structure together and by and by pressing said first flexiblestructure and said second flexible structure together to create a coldwelding between said first flexible structure and said second flexiblestructure.
 24. A capacitor according to claim 23, whereby said laminatedstructure comprises a first flexible structure and a second flexiblestructure, said first flexible structure and said second flexiblestructure being bonded to each other by means of a metal layer, saidmetal layer being applied by applying a metal coating on said firstflexible structure and by applying a metal coating on said secondflexible structure, by bringing the coated surfaces of said firstflexible structure and said second flexible structure together and byand by pressing said first flexible structure and said second flexiblestructure together to create a cold welding between said first flexiblestructure and said second flexible structure.
 25. A capacitor accordingto claim 24, whereby said first flexible substrate and said secondflexible substrate comprise a metal substrate and a ceramic layer, saidceramic layer having a relative dielectric constant ε_(r) higher than 20and a thickness lower than 1 μm.
 26. A superconductor comprising alaminated structure as defined in claim 12.